The invention relates to a device for dewatering and washing fibre stock suspensions by two counter-rotating rolls, a stock feed and a stock discharge, where the headbox is separate at the two rolls and a discharge screw (6) is arranged for filter mat discharge below the gap between the two rolls.
Such systems are known which have a lateral stock feed and a downward-running formation zone, where a fibre mat is formed. This may be followed by a displacement wash zone and a subsequent press nip. Here, the stock discharge takes place above the two rolls into a repulper screw. This type of device shows a number of disadvantages, especially the stock discharge is complicated and susceptible to failure because the repulper vat must be sealed off against the rolls. Furthermore, approximately only half of the circumference is utilized for dewatering and washing. Additionally, this type of device has a tendency toward clogging because the force of gravity attempts to separate the fibre mat from the rolls. Operation without wash water is, therefore, not possible. Devices for fibre stock dewatering are also known from WO 96/06221 A and WO 96/18495, which work in counter-rotation of the rolls versus the devices mentioned. This type of equipment cannot, however, be used for washing. WO 96/06221 A furthermore shows a two-roll press with a stock feed arranged approximately in the area of the horizontal diameter. Thus the maximum range of circumference cannot be used. FR 2 006 772 A also shows the dewatering of a fibre stock suspension on a roll, with two superimposed rolls being represented in FIG. 3. Here, two identical units are placed on top of each other. As a result of the difference in the geodetic height and the joint mat take-off on the lower roll, widely different conditions for the two fibre mats are created before pressing them together in gap 59. The fibre mat therefore has widely different characteristics on the upper and lower sides especially with regard to the dewatering and washing degree. Additionally, in such an arrangement, the stock discharge is not foreseen in the lower section of the rolls but essentially between the 3 o'clock and the 4 o'clock positions.